The Beeholder, January 2009.

Subtitle = Why we fail in Wales

The low population density of Montgomeryshire means that many of us find it easy to maintain genetically isolated stocks. Having the nearest neighbouring beekeeper more than 3 miles away theoretically means that we can select for certain behaviour traits. But research shows that unless we have genetically diverse drones then we may have weak or collapsing colonies. There is anecdotal evidence that in isolated apiaries 5 or fewer hives are not viable in the long term and that the introduction of a swarm from elsewhere seems to give a fillip to the whole apiary. Understanding the genetics of sex determination in the honey bee allows us to understand what may have been happening.

In honeybees males don’t have fathers, queens are promiscuous and bee breeders struggle to develop pure-bred animals – and now we finally understand why.

It was 1845 when a Polish parish priest named Johann Dzierzon discovered that male bees have no fathers . Unfertilized bee eggs, which we now know contain only one set of chromasones (haploidy), develop into males. Fertilised eggs , with two sets of chromasones (diploidy)), become females. Ants and wasps have the same sex determination system, but how it works has been a mystery.

Occasionally, however, it goes wrong, and a fertilised egg develops into a diploid male, whose offspring are sterile. It is these oddments that allow scientists to find the gene responsible. It’s called the Complementary Sex Determinator (csd), the gene works in a completely different way to anything geneticists have discovered before.

There are 19 different variations of the gene. Females have 2 copies whereas males have one. Although the precise mechanism is not yet understood, as long as two different versions of csd are inherited, a female developes from an egg. An unfertilised egg, with just one copy of csd, becomes male (Cell, vol 114, p 419). The system goes wrong when a fertilised egg inherits two copies of the same version of the csd gene. Instead of a female developing the result is a diploid male. Such animals are usually destroyed by the workers at the larval stage.

As beekeepers we try to breed for desirable traits such as, good behaviour, high productivity and disease-resistance but inevitably we are causing inbreeding and the chance that the number of csd variations being reduced. Thus fertilized eggs with two copies of the same csd variation are far more likely to occur. These eggs develop into sterile diploid males. And that means that inbred honeybee colonies quickly die out.

Females probably mate with many males to ensure that they encounter partners with different csd genes and thus avoid producing useless diploid males. Attempts by beekeepers to create pure bred lines have probably failed because there is not enough csd diversity in the strains we create. In the future, it maybe possible for breeders to screen stocks to ensure there is enough csd diversity to keep bees fertile. For further reading try Frontiers in Zoology 2006, 3:1 Single locus complementary sex determination in Hymenoptera: an "unintelligent" design?

Tony Shaw